This invention relates to roll-up doors, and particulary to a roll-up door having a mechanism that will release the bottom of the door from its mountings upon impact against the door and which is a readily returnable to an operating condition after impact.
Roll-up doors are widely used in industry to close off sections of factories or warehouses or to seal a doorway of such a facility that leads to the outside. The doors are typically formed with a flexible fabric curtain or a series of interconnected horizontal slats which together form a flexible curtain. The curtain is usually wound about a drum at its upper end, and a bottom bar extends across the lower free end of the curtain. The lateral sides of the bottom bar typically travel in tracks or channels provided in side jambs or columns forming the frame of the door opening. The curtain drum is powered to roll-up and to unwind the curtain. A counterforce mechanism using either a counter weight or tension springs exerts a force against the bottom bar to maintain the curtain taut.
The roll-up industrial doors are designed to operate very quickly and usually automatically upon the approach of a vehicle to either side of the closed door. However, it happens that the door may not be fully open before a vehicle enters the doorway with the result that the curtain or the bottom bar or both may be struck by the vehicle. This can result in severe damage to the curtain, to the bottom bar, or to the frame, effectively making the door unusable until damaged parts are replaced.
A need exists for a roll-up door that will react to an impact against the curtain or bottom bar by yielding to the force without damaging parts and which can be quickly returned to operating condition. Previous attempts to achieve a break away roll-up door have relied upon a friction fit of parts that may not release when the curtain or bottom bar are struck with a force that is not wholly normal to the plane of the curtain. Also, previous attempts have required extensive and time consuming efforts to prepare the door for reuse.